FIG. 1 illustrates an exemplary basic structure of a UMTS (Universal Mobile Telecommunications System) according to the present invention and the related art.
As shown in FIG. 1, the UMTS includes a terminal (user equipment (UE)), a UTRAN (UMTS Terrestrial Radio Access Network), and a core network (CN). The UTRAN includes one or more radio network sub-systems (RNSs). Each RNS includes a radio network controller (RNC) and a plurality of base stations (Node-Bs) managed by the RNC. One or more cells exist for a single Node B.
FIG. 2 illustrates a radio interface protocol architecture based on a 3GPP radio access network specification between the UE and the UTRAN, and FIG. 3 is an exemplary view showing a process of establishing a connection between RRC layers of the terminal and the UTRAN as shown in FIG. 2.
As shown in FIG. 2, the radio interface protocol has horizontal layers comprising a physical layer, a data link layer, and a network layer. Further, the radio interface protocol has vertical planes comprising a user plane (U-plane) for transmitting data information and a control plane (C-plane) for transmitting control signals (signaling). The protocol layers as shown in FIG. 2 can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on three lower layers of an open system interconnection (OSI) standard model widely known in communication systems.
Each layer in FIG. 2 will be described in more detail as follows.
The first layer (L1), namely, a physical layer, provides an information transfer service to an upper layer by using a physical channel. The physical layer is connected to an upper layer called a medium access control (MAC) layer via a transport channel. Data is transferred between the MAC layer and the physical layer via the transport channel. Meanwhile, between different physical layers, namely, between a physical layer of a transmitting side and that of a receiving side, data is transferred via the physical channel.
Physical channels of the transmitting side and the receiving side include an SCH (Synchronization Channel), a PCCPCH (Primary Common Control Physical Channel), an SCCPCH (Secondary Common Control Physical Channel), a DPCH (Dedicated Physical Channel), a PICH (Paging Indicator Channel), etc.
The PICH is divided into 10 ms-long PICH frames, and a single PICH frame consists of 300 bits. The first 288 bits of a single frame are used for the UE-dedicated PICH. Namely, the first 288 bits are used to transmit one or more UE-dedicated paging indicators (PIs). Here, the UE-dedicated PIs are used to inform a particular UE that a paging message for the particular UE will be transmitted via the PCH. The rear 12 bits of the single PICH frame are not transmitted. Thus, for the sake of convenience, 288 bits corresponding to the front the portion of the PICH channel is defined as a UE PICH, and 12 bits corresponding to the rear portion is defined as a PICH unused part.
The second layer, namely, a data link layer includes a medium access control (MAC) layer and a radio link control (RLC) layer. The MAC layer provides a service to the RLC layer, via a logical channel. The RLC layer of the second layer may support reliable data transmissions and may perform segmentation and/or concatenation on RLC service data units (SDUs) delivered from an upper layer.
A radio resource control (RRC) layer located at the lowest portion of the third layer is defined only in the control plane, handles establishment, reconfiguration and release of radio bearers (RBs), and also handles controlling of transport channels and physical channels. The radio bearer refers to a service provided by the second layer (L2) for data transmission between the terminal and the UTRAN. In general, establishing the radio bearer refers to defining the protocol layers and the characteristics of the channels required for providing a specific service, and configuring respective substantial parameters and operation methods.
Meanwhile, as shown in FIG. 3, in order for the terminal to establish RRC connection with the UTRAN, an RRC connection procedure should be performed. The RRC connection procedure is as follows. When the terminal transmits an RRC connection request message to the UTRAN (S11), the UTRAN transmits an RRC connection setup message to the terminal (S12), and the terminal transmits an RRC connection setup complete message to the UTRAN (S13).
As shown in FIG. 3, an idle state and an RRC connected state exist according to the RRC connection as shown in FIG. 3.
The RRC connected state refers to a state of the terminal in which the RRC layer of the terminal and that of the UTRAN are connected to exchange an RRC message to each other. The idle state refers to a state of the terminal in which the RRC layer of the terminal and that of the UTRAN are not connected.
The RRC connected state may be classified into a URA_PCH state, a CELL_PCH state, a CELL_FACH state and a CELL_DCH state.
When the terminal is in the CELL_DCH state or in the CELL_FACH state, the terminal continuously receives data from the UTRAN. If, however, the terminal is in an idle state, in a URA (UTRAN Registration Area)—PCH state, or in the CELL_PCH state, in order to reduce power consumption, the terminal discontinuously receives a PICH (Paging Indicator Channel) which is a physical channel, an SCCPCH (Secondary Common Control Physical Channel) which is a physical channel (a PCH (Paging Channel) which is a transport channel is mapped to the SCCPCH) by using a DRX (Discontinuous Reception) method. During other time intervals than the time duration while the PICH or the SCCPCH is received, the terminal is in a sleeping mode.
In the related art, the terminal using the DRX method wakes up in the sleeping mode at every CN domain specific DRX cycle length or at every UTRAN specific DRX cycle length to receive the UE-dedicated PI (Paging Indicator) on the PICH channel. Here, the UE-dedicated PI in the related art is used to inform a particular UE that a paging message for the particular UE will be transmitted to the particular UE via the PCH channel.
Meanwhile, the terminal using the DRX method uses DRX of two types of lengths. Namely, the terminal uses a long DRX and a short DRX. Thus, the terminal in the CELL_PCH may periodically receive a downlink channel according to the long DRX period or a short DRX period to check whether there is data for the terminal. In detail, the terminal first operates according to the long DRX period, and immediately when downlink data is received, the terminal is changed to operate according to the short DRX period and monitors a downlink channel at every short DRX period.
As described above, in the related art, the terminal operates according to the long DRX period until before it receives downlink data, and immediately when the terminal receives the downlink data, it is changed to operate according to the short DRX period and monitors the downlink channel at every short DRX period. After changed to operate according to the short DRX period, if the terminal receives downlink data within a predetermined time, it continuously maintains to be operated according to the short DRX period. If, however, the terminal fails to receive downlink data within the predetermined time after changing to operate according to the short DRX period, the terminal is changed to operate according to the long DRX period.
However, the related art has the following problem. That is, if the UTRAN transmits the downlink data to the terminal operating according to the long DRX period but the terminal does not properly receive the downlink data, the UTRAN will determine that the terminal operates according to the short DRX period but the terminal actually operates according to the long DRX period.